Separation of highly branched paraffins into odorless fractions



c. CRAWFORD ET AL 2,463,601 SEPARATION OF HIGHLY BRANCHED PARAFFINS IN 0 ODORLESS FRACTIONS Filed Sept. 21, 1945 March 8, 1949.

ATTORNEYS Patented Mar. 8, 1949 GHLY BRANCHED PAR- SEPARATION OF HI AFFINS INTO OD ORLESS FRACTIONS Chester 0. Crawford and Lloyd 0. Morris, Bartlesville, Okla., assignors to Phillips Petroleum Application September 21,

Company, a corporation of Delaware 1945, Serial No. 617,870

2 Claims. (Cl. 196-73) This invention relates to improvements in methods for separating mixtures of highly branched paraffin hydrocarbons into substantially odorless fractions having definite boiling ranges.

In processes for the manufacture of highly branched paraffin hydrocarbons for high octane motor fuel considerable quantities of such hydrocarbons boiling above but overlapping th motor fuel range are recovered as by-products. This is especially true of processes of catalytic alkylation wherein an isoparafiin and a low-boiling olefin are reactants, and/or processes for the manufacture of diisopropyl wherein isobutane is alkylated with ethylene in the presence of a suitable catalyst.

An obvious possible use of these by-products would be their employment as solvents in the dry cleaning, printers ink, paint and insecticide industries, but when it is attempted to separate these by-products into fractions of suitable boiling range by conventional fractional distillation methods it is found that the odors of the resulting fractions make them unfit for use in such commercial applications.

Odorous solvents are especially objectionable in the dry cleaning, paint and insecticide industries. If alkylate fractions are to be saleable for such use they must be able to compete successfully with deodorized straight run naphthas on the basis of odor.

The highly branched paraffin hydrocarbons are most commonly made by catalytic alkylation of low-boiling isoparafins with low-boiling olefins in the presence of a suitable alkylation catalyst, such as concentrated sulfuric acid or substantially anhydrous hydrofluoric acid. They may be made by the alkylation of isobutane with ethylene to give principally diisopropyl. This type of alkylation is usually effected with an aluminum halide complex catalyst promoted with small amounts of hydrogen halide such as HCl. A method for preparing diisopropyl in this manner is shown in the copending application of Clarence R. Ringham, Serial No. 556,208, filed September 28, 1944, now Patent 2,409,389, issued October 15, 1946. However, the present invention is applicable to mixtures of highly branched paraffin hydrocarbons prepared in any manner, since the presence of large numbers of tertiary and/or secondary carbon atoms supplies the condition necessary for the development of disagreeable odors in these materials.

It is common practice in the manufacture of these highly branched paraffin hydrocarbons to purify the feed stocks to a very high degree in order to obtain maximum catalyst life. Such feed stocks are practically free from sulfur, nitrogen, oxygen and other contaminants and yield highly branched paraffin products which have extremely low odor intensity.

When substances boiling in the motor fuel range are distilled from a mixture of highly branched parafiins a kettle product is obtained which is practically odorless. It was therefore very surprising to find that all fractions taken overhead from this kettle product by conventional distillation methods had rancid, disagreeable odors and that this odor could not be eliminated overhead by increasing the degree of fractionation except in the absence of oxygen. This is true whether the distillation be performed continuously or in batches; at atmospheric pressure, with steam, or under vacuum. The kettle prodnot itself was found to develop odor in storage or on boiling.

The reactions by which the odorous compounds are formed have not been completely understood but it is known that olefin formation is not a major cause since the bromine number of the hydrocarbon is not increased by distillation.

Since it is impossible to eliminate the odor overhead when the distillation system contains air or when the incoming feed contains dissolved oxygen and we have found that odor is present in any fraction of distillate through which vapors from such oxygen containing feed passes, as it does on a plate of a fractionation column, it seems probable that the odorous materials are formed by reactions involving oxidation, which continue so long as the incoming feed contains dissolved oxygen, and since the kettle product is odorless that the odorous products are sufficiently volatile to be carried onward by the vapor stream. This is a purely theoretical attempt to rationalize the peculiar behavior of these substances and we do not wish to limit our invention to any theory or mechanism of chemical action.

It is a principal object of this invention to provide a method whereby mixtures of highly branched paraffin hydrocarbons boiling above, but overlapping the motor fuel range, may be separated into substantially odorless fractions having definite boiling range.

Numerous other objects and features of novelty will become apparent to those skilled in the art as this disclosure proceeds.

Our invention consists of the discovery odorous materials developing during such distillation are principally products resulting from that spirit and scope of this invention. A mixture of highly branched paraiiin hydrovery'fivolatile.

carbons obtained as a kettle product from. the After collecting the fractions of distillate undistillation of at least a portion of the hydroderinert substantially odorless gas in suitable carbons boiling in the motor fuel range from the storage flanks, the fractions may be stored for I into pretreating tank 2 When tank 2 1s suitthat the blanketing with inert gas 1s maintained a y fi ed leaving a Vacant Space n e pper dur ng such time of stoi age or a suitable oxidap f he nk an nert gas such as nitro n, tron inhibitor is added to the product. hydrogen, methane or other substantially odorgo less gas or mixture of gases containing substan- Example tially no oxygen is admitted via lines 3 and 4 and an open coil 5 1n the bottom portion of tank 2 H avy alkylatc, shipped to the refinery y t suificient pressure to cause Vigorous agitation of phc lc pr ssure and was blown with an inert, subthe liquid in tank 2. This agitation and blowing stantially odorless gas composed of 50% hydrowith inert'gas is continued at room temperature gen, 48.5% meth e an ethane for a period for a period of time up to three hours, depend- Of; about /2 hours at room temperature. The

to oxygen prior to this step. During this period duced into the distillation system and displaced until substantially all air is driven out of the tankthe alkylate was pumped through a rate of be introduced into the storage tanks to replace tion with an initial boiling point of 325 F. and an the air contained therein. end point of 375 F. The feed rate to this column suitable condensers, connections and any auxpounds per day to give kettle temperatures rangiliary apparatus desired, the valve 7 is opened ing from 360 F. to 370 F. The top of the column and the hydrocarbon mixture in tank 2, now subthen operated at atemperature of from 310 F. stantially free from oxygen, 1s introduced via line to 320 F and at a pressure of 2 to 4 p S 1 g he II into a medial point in the distilling column l2 overhead product passed through a pressure reintroduction of inert gas through the open coils was collected as liquid in an accumulator operat- IG and I5 is continued so that there IS a coning at atmospheric pressure and kept blanketed tmuing blanketing by inert gas during dlstillawith inert odorless gas to prevent contamination t1on A high-boiling fraction from which odorof the overhead product with an From this acthe lower portion of column 22. flow controller and preheater to serve as reflux.

The distillation may be conducted otherwise A'second hydrocarbon stream controlled by liquid in any conventional manner, except that steam, level in the accumulator was removed to a deif used, must be taken from an oxygen-free hydrator for further removal of water. This desource. hydrating vessel was also kept blanketed with Duringdistillation of the contents of pretreatinertgas. The final product was withdrawn to ment tank 2 pretreatment tank 8 may be filled storage blanketed by inert odolless gas The and blown with men: gas to deoxygenate its confinal product had a boiling range of from 35 F is emptied. Tank 2 is then refilled and the cycle boiling point obtained and that intended was in sufiicient inert gas to blanket any accumulators the system atthe beginning of distillation. Duror surge tanksso that no air may enter the sysing the distillation test samples were withdrawn tem. I from each plate of the fractionating column. A

When the hydrocarbon feed has been exposed definite odor gradient was found between the to air for some time,- as mayoccur during trans- 19th-and20th plates-at the beginning-of distilla tion. No odor was detected below the 17th plate at any time. The 1700 gallons of final product were so nearly odorless that distilled water was used as the basis of comparison.

The term inert substantially odorless gas as used in this specification refers to any gas or mixture of gases which is substantially odorless and which is inert insofar as reactions resulting in formation of odorous compounds from highly branched paraffin hydrocarbons are concerned.

We claim:

1. An improved process for producing an odorless normally liquid branched-chain paraffin hydrocarbon fraction from an olefin-free normally liquid parafilnio' charge stock containing said paraffin hydrocarbons together with dissolved oxygen and odorous oxygen-containing products resulting from reaction of branched-chain paraifin hydrocarbons with dissolved oxygen, said charge stock being free from sulfur and nitrogen compounds, which comprises bubbling through a liquid body of said charge stock an inert, odorless, oxygen-free gas until all dissolved oxygen is removed from said charge stock, passing a stream of said deoxygenated charge stock to an intermediate point of a first fractional distillation column up through which 1s passing a stream of free-oxygen-free inert odorless gas, removing an odorous distillate from said first column and discharging same from the process, passing a kettle product from said first column to a second fractional distillation column up through which is passing a stream of free-oxygen-free inert odorless gas, recovering an odorless distillate comprising normally liquid branched-chain parafiin hydrocarbons as a product of the process.

2. An improved process for producing an odorless normally liquid branched-chain paraifin hydrocarbon fraction from an olefin-free normally liquid paraffinic charge stock containing said paraffih hydrocarbons together with dissolved oxygen and odorous oxygen-containing products resulting from reaction of branched-chain paraffin hydrocarbons with dissolved oxygen said charge stock being free from sulfur and nitrogen compounds, which comprises bubbling through a liquid body of said charge stock an inert, odorless, oxygen-free gas until all dissolved oxygen is removed from said charge stock, passing said deoxygenated charge stock to a fractional distillation means which is free from free oxygen, distilling said charge stock in said means with continuous introduction of oxygen-free odorless inert gas into and up through said means during said distillation, initially removing and discharging an odorous distillate comprising aforesaid oxygenated products, subsequently removing an odorless distillate comprising normally liquid branched-chain parafiin hydrocarbons, and storing said odorless distillate under a blanket of oxygen-free, odorless inert gas.

CHESTER C. CRAWFORD. LLOYD C. MORRIS.

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